The present invention relates to a pattern formation method for forming a pattern by controlling liquid repellency and lyophilic properties, particularly to a pattern formation method for forming a pattern having a flat surface by preventing dewetting of a liquid film from occurring.
In recent years, techniques to form wiring of electronic circuits and micropatterns such as electric wiring patterns on substrates have been drawing attention. A liquid discharge head of an inkjet system (inkjet head) is used for the formation of such a micropattern, for example. In this case, droplets of liquid having metal particles or resin particles dispersed therein are jetted from the inkjet head to draw a pattern, and the liquid is cured by heating, thereby forming an electric wiring pattern.
Currently, in some cases, a liquid-repellent film is formed on a flexible substrate (support) such as PET or PEN, and wiring of an electronic circuit and a micropattern such as an electric wiring pattern as described above is formed on the liquid-repellent film. Such a micropattern is used to form a gate electrode, a source electrode and a drain electrode of a thin film transistor (hereinafter called “TFT”).
JP2009-26901 A discloses a laminated structure composed of a substrate, a wettability changeable layer, a conductive layer and a semiconductor layer. The wettability changeable layer is a layer in which the critical surface tension (also called “surface free energy”) varies due to imparted energy such as heat, ultraviolet light, an electron beam and plasma, and has formed thereon a high surface energy portion where the critical surface tension (surface free energy) is relatively high and a low surface energy portion where the critical surface tension (surface free energy) is relatively low. The conductive layer is formed at the high surface energy portion while the semiconductor layer is provided so as to be in contact with at least the low surface energy portion.
As a result of ultraviolet irradiation, the wettability changeable layer changes into the high surface energy portion due to the imparted energy and at the same time, the thickness of the wettability changeable layer is slightly reduced. This thickness reduction causes a level difference at the boundary line between the high surface energy portion and the low surface energy portion, and the level difference serves as a bank.
In JP2009-26901 A, lyophilic ink is discharged to the high surface energy portion that is a lyophilic surface by an inkjet method. At this time, the lyophilic ink hits the surface and wet-spreads thereon. However, in JP2009-26901 A, a three-dimensional level difference is formed at the boundary between the high surface energy portion and the low surface energy portion and therefore, the ink can be prevented from running off to the low surface energy portion area. As a result, a pattern (conductive layer) can have an excellent edge shape, and electron elements having the uniform characteristics can be fabricated.
As disclosed in JP2009-26901 A, in the case where a pattern (conductive layer) is formed using the hydrophilic/hydrophobic variable layer (wettability changeable layer) in which, upon receipt of energy such as ultraviolet light, the portion applied with the energy is caused to be lyophilic (high surface energy portion) and the film thickness of the portion is reduced, a pattern (conductive layer) can be formed as described below.
First, a lyophilic/lyophobic variable layer 122 that is originally liquid-repellent is formed on a support 120 as shown in FIG. 13A. Then, the lyophilic/lyophobic variable layer 122 is irradiated with, for instance, ultraviolet light to form a liquid-repellent portion 122a and a lyophilic portion 122b. Due to the ultraviolet irradiation, a level difference arises between the liquid-repellent portion 122a and the lyophilic portion 122b. When a liquid film 124, which is to be a pattern (conductive layer), is formed to have a uniform thickness under this condition, a level difference arises also at the surface of the liquid film 124 in accordance with the level difference of the underlayer. Hence, the liquid film 124 having an uneven surface is formed. The liquid film 124 having the uneven surface is formed because the surface reflects the level difference of the underlayer between the liquid-repellent portion 122a and the lyophilic portion 122b. 
Thereafter, the liquid film 124 is repelled by the liquid-repellent portion 122a so that a pattern (conductive layer) 126 as shown in FIG. 13B is formed.
Alternatively, as shown in FIG. 14A, a lyophilic/lyophobic variable layer 122 that is originally liquid-repellent is formed on a support 120. Then, the lyophilic/lyophobic variable layer 122 is irradiated with, for instance, ultraviolet light to form a liquid-repellent portion 122a and a lyophilic portion 122b. In this example, there is no level difference between the liquid-repellent portion 122a and the lyophilic portion 122b and the surface is flat. When a liquid film 124, which is to be a pattern (conductive layer), is formed to have a uniform thickness under this condition, the liquid film 124 having a flat surface is formed.
Thereafter, the liquid film 124 is repelled by the liquid-repellent portion 122a so that a pattern (conductive layer) 126 as shown in FIG. 14B is formed.